1. Field of the Invention
This invention lies in the field of apparatus for pumping liquids from deep boreholes, such as deep water or oil wells. More particularly, it concerns a type of deep well pump in which a continuously driven hydraulic pump in a down-hole assembly provides motive power to drive a reciprocating hydraulic pump in which one cylinder and piston provides the force to drive a second smaller cylinder and piston, to pump liquid up the tubing.
Still more particularly this invention relates to a method by which a high pressure accumulator acts as a storage of energy during one part of the pumping cycle in which liquid is not lifted from the borehole, and the accumulator applies its stored energy to aid the hydraulic pump in the other part of the pumping cycle in which liquid is lifted from the borehole.
2. Description of the Prior Art
In the prior art there are instances where hydraulic pumps have been placed in a deep borehole, hung on tubing, in which a hydraulic pump at the surface supplied pressurized liquid to the down-hole pump in order to pump well liquids up the tubing. This case is different from the situation where sucker rod pumps ae used, with surface mechanical pumping equipment in which a mechanical counterbalance can be utilized to average out the irregular pumping force required in the two-part pumping cycle, in which the sucker rods are lowered, and then lifted, carrying the pumped liquid. The hydraulic systems in the prior art have not utilized a counterbalance equivalent. This causes a highly variable pumping force requirement and necessitates a larger size of engine to drive the system, and so on. The counterbalance in this instance is provided by a high pressure hydraulic accumulator which accepts and stores energy during the part of the pumping cycle in which little energy is required from the hydraulic pump and on the next part of the cycle, delivers the stored energy to assist the hydraulic pump.